In order to elucidate the electrochemical properties of iron rust, galvanostatic cathodic polarization of rusted steel and rust electrodes, prepared by fixing a piece of rust plate on an acrylic plate with conductive adhesive, was examined. The change in the amount of crystalline substances, in the rust layer was observed by X-ray diffraction. The electrochemically active intermediate substances, could not be identified by X-ray diffraction, but their behavior was distinguished from that of crystalline substances. The rest potential of the rust electrode was controlled by the equilibrium potential of intermediate substances. An overlapping dual electrode model is proposed for rusted steel in aqueous solution. Beneficial elements added to weathering steel inhibit the formation of crystalline magnetite in the cathodic reduction process of rust and increase the electrical resistance of the rust layer.